theory, in music, discipline involving the construction of cognitive systems to be used as a tool for comprehending musical compositions. The discipline is subdivided into what can be called speculative and analytic theory. Speculative theory engages in reconciling with music certain philosophical observations of man and nature. It can be prescriptive when it imposes these extramusical contentions to establish an aesthetic norm. Music theory tended toward this aspect until the 20th cent. An example is the attempt to assert the superiority of tonal music over other systems by reference to the relationship of the triad to the natural overtone series. Analytic theory, on the other hand, undertakes detailed study of individual pieces. Analyses of compositions of a particular genre are synthesized into a general system, or reference, against which the individuality of these pieces can be perceived. In more general usage the term theory is used to include the study of acoustics, harmony, and ear training. In ancient Greece music theory was mainly concerned with describing different scales (modes) and their emotional character. This theory was transmitted, largely erroneously, to medieval Europe by the Roman philosopher Boethius in his De musica (6th cent. AD). Medieval European theory dealt with notation, modal and rhythmic systems, and the relation of music to Christianity. Gioseffo Zarlino (1515–90) was the first to consider the triad as a compositional reference. In the 18th cent. Jean Philippe Rameau sought to show how the major-minor system of tonal harmony derives from the inherent acoustical properties of sound itself, and establish the laws of harmonic progression. The writings of Heinrich Schenker are among the most important in the sphere of tonal theory. Major contemporary theorists are Paul Hindemith, who propounded the idea of non-triadic pitch centrality, and Milton Babbitt, who has published revealing explications of twelve-tone music.